Nitrogen- and ceramic-surface-treated components for downhole motors and related methods

A method of making a downhole tool for earth-boring applications, comprising:

• exposing a component of the downhole tool to an elevated temperature to heat the component in a nitrogen-rich environment, the component comprising an inner bore extending at least partially through the component, the inner bore being defined by an inner surface of the component;
• diffusing nitrogen into a steel material of the component to form a nitrided region on the interior surface of the component, the nitride region comprising a first portion exhibiting a first concentration of nitrogen and a second portion adjacent to the first portion, the second portion exhibiting a second, lower concentration of nitrogen;
• cooling the component from the elevated temperature;
• removing the component from the nitrogen-rich environment;
• and
• coating a ceramic material on the nitrided region of the inner surface of the component.